The aqueous polyurethane resin dispersion can provide a coating film having adhesiveness, wear resistance and rubbery properties, and is an environmental consideration type material which can reduce a volatile organic material as compared with the conventional solvent type polyurethane, so that it is a material that replacement from the solvent type polyurethane has been progressed.
A polycarbonate polyol is a useful compound which can become a starting material of a polyurethane resin, and a polyurethane resin having durability to be used for a rigid foam, a flexible foam, a paint, an adhesive, synthetic leather, ink binder and the like, can be produced by the reaction with an isocyanate compound. It has been stated that the characteristic feature of the polyurethane resin obtained by using the polycarbonate polyol has been produced by high cohesive force of the carbonate group, and as compared with the case where the polyether polyol or the polyester polyol is used, it is excellent in hydrolysis resistance, heat resistance, oil resistance, elastic recovery, wear resistance and weather resistance (see Non-Patent Document 1). Also, it has been known that a film obtained by an aqueous dispersion type polycarbonate polyurethane resin composition is excellent in light resistance, heat resistance, hydrolysis resistance and oil resistance (see Patent Document 1).
The present inventors have already found out that an aqueous polyurethane resin dispersion having urethane bonds, urea bonds and carbonate bonds and having a blocked isocyanato group with a specific amount can control a film preparation rate after coating, is capable of redispersing the coating film in water, and the coating film obtained by coating and heat treatment is excellent in water resistance and solvent resistance, excellent in adhesiveness to an electrodeposition film, and excellent in impact resistance since a breaking energy at tension is high (see Patent Document 2).
As a means to heighten storage stability of the aqueous polyurethane resin dispersion, it has been known a means that a three-dimensional cross-linking is introduced by the reaction of a polyfunctional amine having three or more amino groups per molecule and an isocyanate (see Patent Document 3 and Patent Document 4).
On the other hand, to the aqueous polyurethane resin dispersion, an additive such as various pigments is added in some cases. When a pigment difficulty dispersed in an aqueous medium is to be added, a non-aqueous organic solvent is generally added to the aqueous resin dispersion as a dispersant with the pigment (see Patent Document 5). However, when the non-aqueous organic solvent is added to the aqueous polyurethane resin dispersion, a viscosity of the aqueous polyurethane resin dispersion is increased, and problems such as deterioration of handling property and reduction of discharge property when spraying have occurred.